1. Field of the Invention
This invention relates to ultrasound imaging systems.
2. Description of the Prior Art
Ultrasound imaging systems are attractive for medical applications because they permit imaging of internal structures of the body without the use of harmful forms of radiation. Numerous proposals have been made for such systems and many are in actual use. Although the systems vary widely in detail, most known systems basically utilize an ultrasonic transducer or bank of transducers to beam pulses of ultrasound into a structure to be imaged and to receive reflections of those pulses. The beamed pulses are directed through the structure to be imaged in a suitable scanning pattern by mechanical and/or electronic means.
A major problem with such systems is lack of resolution in lateral directions. Some improvement can be obtained utilizing large aperture transducers which are electronically or acoustically focused but this improvement is at the expense of a very shallow depth of field. Consequently sophisticated means are required to maintain focus throughout a scan, and the operation of such means tends to limit the rate of scan and thus increase the time taken to generate an image. Even with such means, resolution is often inadequate for reliable detection of small anomalies in the structure being imaged.
An example of a known type of B-scanning ultrasonic system is disclosed in U.S. Pat. No. 4,014,207, issued Mar. 29, 1977, to Meyer, et al., for SECTOR SCANNING ULTRASONIC INSPECTION APPARATUS.